There's enough hesitation that Sans keeps hold of his cool, willing himself to behave like Papyrus. Any amount of good, it's worth holding onto. Might even be a seed of something worth nurturing, even if Sans wasn't the one to do it.

After all, Sans was still trying to keep from throwing Rinzler against the wall. Luckily, he's had infinite revolutions of time to hone his patience.

"Can I ask who taught you to have such little respect for life? Taught, programmed, showed, whatever the word... seems like, in my brother's words, something pretty awful must've happened for you to act with so much hate." Sans kicked back against the far wall, expression even. "Lay it on me. I don't claim to judge."